The present invention relates to a headbox for delivering a jet of stock to a forming zone in a former for wet-forming a fiber web, and relates more particularly to the mounting of vanes within a slice chamber of a multi-layer headbox via an arrangement that allows each vane to pivot about its attachment to a turbulence generator of the headbox.
In papermaking, a web is formed in a former of the papermaking machine by delivering a jet of papermaking stock from a headbox to a forming zone of the former. A headbox generally comprises a slice having a slice chamber and a slice opening, and a turbulence generator that includes a plurality of turbulence channels that open out into the slice chamber for delivering stock into the slice chamber. Within the slice chamber, the flow of stock is divided into a plurality of separate channels by vanes that are mounted in the slice chamber, each vane typically being mounted to an elongate anchoring element arranged between adjacent rows of turbulence channels of the turbulence generator. The anchoring element typically has a continuous engagement groove that is open towards the slice chamber to facilitate mounting the vane to the anchoring element.
SE-511 684 C2 describes a multi-layer headbox with vanes that each have a connection bar with a flexible engagement part for pivotable journaling of the vane to an anchoring element that is fixedly arranged between two rows of turbulence channels. The headbox is of the rectilinear type, i.e., at least the intermediary channels extend in line with the turbulence channels. However, the described fastening of the vane directly to the anchoring element is not suitable in the case of a headbox of the angled type, in which all the vanes and channels in the slice chamber extend at an angle to the turbulence channels, as the axis of pivot is located inside the anchoring element such that the pivoting capacity of the vane would be insufficient, and the vane and connection bar are too close to the opening of the turbulence channel. Furthermore, the described fastening is not applicable in the case of an anchoring element having a dovetail-shaped groove for the connection bar.
Various solutions have been suggested for mounting a vane aligned at an angle to an anchoring element in a turbulence generator. U.S. Pat. No. 4,133,715 describes turbulence vanes that each have a connection bar consisting of a flexible material and having an extended intermediate part and a wedge-shaped engagement part that is received in a dovetail groove. A change in the position of the vane, due to differences in pressure between the two channels separated by the vane, result in corresponding bending of the long intermediate part. Repeated bending results in flexure fatigue in the material and a risk of the intermediate part fracturing. The bending of the intermediate part also causes the vane to be displaced in its plane so that the downstream end of the vane changes its position relative to the slice opening in proportion to the magnitude of the bending of the intermediate part. Such a change in position of the downstream edge is not acceptable in respect of a stock-separating vane in a multi-layer headbox, as it would affect the layers of the jet of stock detrimentally in the proximity of the slice opening.
WO 98/50625 describes vanes that each have a connection bar made of stainless steel. The connection bar has an extended intermediate part that is curved to retain the vane at an angle to the turbulence channel. The engagement part of the connection bar is dovetail-shaped to co-operate securely with the dovetail groove in the engagement part to provide a rigid joint. It will be appreciated that the vane and the connection bar are subjected to significant and repeated strains when differences in pressure arise between the two channels that are separated by the vane, so that there is a significant risk of a fracture occurring in the vane adjacent to the connection bar and/or in the connection bar, especially at the root of the dovetail-shaped engagement part. The last-mentioned document acknowledges the problem with such a rigid anchoring of the vane and therefore suggests a modified connection bar, the engagement part of which is fashioned with a circular cross section to form a joint so that the vane can pivot. A potential pivoting of the vane results in a change in position of the downstream edge of the vane, which is not acceptable for a stock-separating vane in a multi-layer headbox. However, it will be appreciated, of course, that the pivoting function is lost after a relatively short period of operation, as the circular joint will get wedged and assume a stationary position impervious to pivoting, which wedge locking occurs because of the tensile forces created by the stocks in the vane. Accordingly, the modified connection bar will function in the same unsatisfactory way as the first described connection bar with the rigid dovetail joint.
When a vane and/or its connection bar with the fastening systems described above has (have) been damaged, there has hitherto been no alternative and better arrangement for the mounting of the vane to reduce the operational disruptions and replacements. This applies particularly to headboxes where the anchoring elements of the turbulence generator are provided with dovetail grooves and the vanes are positioned at an angle relative to the turbulence channels.
Further suggestions for fastening a vane to a turbulence generator are described in SE-440 924, U.S. Pat. No. 4,617,091, U.S. Pat. No. 4,941,950, and U.S. Pat. No. 5,013,406.
The present invention addresses the problems mentioned above and seeks to provide a mounting arrangement for the vanes of the headbox that is simple in its construction and easy to install and which reduces the risk of damage to the vanes and their potential connection bars. The invention offers a simple and reliable way to replace existing fastening systems with a mounting arrangement in accordance with the invention, for instance in connection with re-construction of an already installed headbox. A headbox and mounting arrangement in accordance with the invention includes a slice defining a slice chamber and a slice opening, at least one vane arranged in the slice chamber to divide the flow of stock into at least two separate channels, a turbulence generator defining a plurality of turbulence channels corresponding to the number of channels in the slice chamber, each turbulence channel feeding stock to one of the channels in the slice chamber, the turbulence generator having an anchoring element for each vane, each anchoring element being arranged between adjacent turbulence channels, and a mounting arrangement for mounting each vane to the corresponding anchoring element. The mounting arrangement comprises a coupling element disposed at an upstream end of the vane, and an assembly bar extending along the anchoring element and adapted to receive the coupling element of the vane.
In accordance with one preferred embodiment of the invention, the headbox, as well as the mounting arrangement, is characterized in that the assembly bar has
a protrusion that is arranged to be received in the engagement groove of the anchoring element to form a rigid joint and
a continuous journaling groove that is arranged at a pre-determined distance from the anchoring element and is open towards the vane by way of a side opening, and has opposite pivot surfaces, and that the pivot member of the vane is arranged to be received in the journaling groove to co-operate with its pivot surfaces to form an axis of pivot.
In accordance with the invention, the method is characterized in that an assembly bar, having a longitudinal protrusion with a cross section adapted to said pre-determined cross section of the engagement groove, is brought into engagement, by way of said protrusion, with the engagement groove of the anchoring element so that a butt, bending resistant joint is formed therebetween, and in that the pivot member of the vane is brought into engagement with an elongate journaling groove in the assembly bar to cooperate with opposite pivot surfaces in the journaling groove to form an axis of pivot, the vane pivoting about the same.